Improve number->string conversion

[bnoordhuis]

The results from test262/implementation-contributed/v8/mjsunit/number-tostring.js suggest there is room for improvement:

5a.1eb851eb852 !== 90.12, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:77:32)                                                   
0.1999999999999a !== 0.1, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:78:34)                                                   
0.028f5c28f5c28f6 !== 0.01, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:79:35)                                                 
0.032617c1bda511a !== 0.0123, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:80:35)                                               
605f9f6dd18bc8000 !== 111111111111111110000, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:81:35)                                
3c3bc3a4a2f75c0000 !== 1.1111111111111111e+21, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:82:36)                              
25a55a46e5da9a00000 !== 1.1111111111111111e+22, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:83:37)
0.0000a7c5ac471b4788 !== 0.00001, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:84:38)                                           
0.000010c6f7a0b5ed8d !== 0.000001, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:85:38)    
0.000001ad7f29abcaf48 !== 1e-7, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:86:39)                                             
0.000002036565348d256 !== 1.2e-7, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:87:39)                            
0.0000021047ee22aa466 !== 1.23e-7, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:88:39)                                          
0.0000002af31dc4611874 !== 1e-8, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:89:40)                                            
0.000000338a23b87483be !== 1.2e-8, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:90:40)                                          
0.00000034d3fe36aaa0a2 !== 1.23e-8, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:91:40)                                         
-5a.1eb851eb852 !== -90.12, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:96:33)                                                 
-0.1999999999999a !== -0.1, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:97:35)                                                 
-0.028f5c28f5c28f6 !== -0.01, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:98:36)                                               
-0.032617c1bda511a !== -0.0123, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:99:36)                                       
-605f9f6dd18bc8000 !== -111111111111111110000, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:100:36)                             
-3c3bc3a4a2f75c0000 !== -1.1111111111111111e+21, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:101:37)                          
-25a55a46e5da9a00000 !== -1.1111111111111111e+22, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:102:38)
-0.0000a7c5ac471b4788 !== -0.00001, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:103:39)
-0.000010c6f7a0b5ed8d !== -0.000001, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:104:39)
-0.000001ad7f29abcaf48 !== -1e-7, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:105:40)                           
-0.000002036565348d256 !== -1.2e-7, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:106:40)        
-0.0000021047ee22aa466 !== -1.23e-7, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:107:40)
-0.0000002af31dc4611874 !== -1e-8, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:108:41)
-0.000000338a23b87483be !== -1.2e-8, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:109:41)
-0.00000034d3fe36aaa0a2 !== -1.23e-8, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:110:41)
100000000000080 !== 72057594037928060, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:123:33)
1000000000000100 !== 1152921504606847200, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:124:34)
1000000000000000 !== 1152921504606847000, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:125:34)
1000000000000000 !== 1152921504606847000, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:126:34)
100000000000000000000000000000000000000000000000010000000 !== 72057594037928060, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:127:75)
-100000000000080 !== -72057594037928060, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:132:34)
-100000000000000000000000000000000000000000000000010000000 !== -72057594037928060, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:133:76)
8.8 !== 8.5, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:144:21)
-8.8 !== -8.5, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:145:22)
1.1 !== 1.3333333333333333, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:147:21)
11.1 !== 4.333333333333333, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:148:22)
0.01 !== 0.1111111111111111, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:149:22)
10000.01 !== 81.11111111111111, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:151:32)
0.0212010212010212010212010212010212 !== 0.2857142857142857, at <eval> (test262/implementation-contributed/v8/mjsunit/number-tostring.js:152:54)

// assertEquals.js
function assertEquals(a, b) {
    if (String(a) !== String(b)) print(`${a} !== ${b}, ` + new Error().stack.split(/\n\s+/)[1].trim())
}

run as:

$ ./qjs -I assertEquals.js test262/implementation-contributed/v8/mjsunit/number-tostring.js